netdev - Re: Re: Re: limited network bandwidth with 3.2.x kernels

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Message-ID: <CADVnQykmt7yaENfgVAs521EX4fBjYbJqNEo2pTDuC8jmnivbuA@mail.gmail.com>
Date:	Fri, 17 Feb 2012 11:55:02 -0500
From:	Neal Cardwell <ncardwell@...gle.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	alekcejk@...glemail.com, netdev@...r.kernel.org
Subject: Re: Re: Re: limited network bandwidth with 3.2.x kernels

And thanks, Alexey, for the detailed info.

The first tcpdump shows a SYN/SYNACK RTT of roughly 64ms, and the
second tcpdump shows a steady-state receive window of 21177* 16=338832
bytes. Together those imply that the receiver window is limiting
bandwidth to roughly (21177 * 16 bytes)/ 0.064sec ~= 5.0 Mbytes/sec.
This is pretty close to the throughput of 4.9Mbytes/sec that wget
reports, suggesting that indeed the receiver window was the limiting
factor here.

And Eric's proposed fix for this receiver window issue sounds like it
should take care of this.

neal
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